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A colorimetric method for the estimation of the total content of cannabinoids in cannabis samples is proposed. The assay is based on the reaction of these compounds with the reagent Fast Blue B (FBB), which has been immobilized into polydimethylsiloxane (PDMS). The reaction and detection conditions have been established according to the results obtained for the individual cannabinoids Δ 9 -tetrahydrocannabidiol (THC), cannabidiol (CBD), and cannabinol (CBN), as well as for ethanolic extracts obtained from cannabis samples after ultrasonication. In contact with the extract and under basic conditions, the reagent diffuses from the PDMS device, producing a red-brown solution. The absorbances measured at 500 nm after only 1 min of exposure to the FBB/PDMS composites led to responses proportional to the amounts of the cannabinoids in the reaction media. Those absorbances have been then transformed in total cannabinoid content using CBD as a reference compound. The potential utility of the proposed conditions has been tested by analyzing different cannabis samples. The selectivity towards other plants and drugs has been also evaluated. The present method is proposed as a simple and rapid alternative to chromatographic methods for the estimation of the total content of cannabinoids.

The development of methodologies using inexpensive, fast, and reliable instrumention is desirable in illicit drug analysis. The purpose of this study was based on cyclic voltammetry technique to differentiate the electrochemical behavior of ∆(9) -THC, the psychoactive substance in marijuana, and five different extract plants to yield false positive results after analysis protocol for cannabinoids using thin-layer chromatography and Fast Blue B salt. After applying a deposition potential of -0.5 V in a glassy carbon working electrode, the results indicated an anodic peak current at 0.0 V versus Ag/AgCl after addition of ∆(9) -THC solution in the electrochemical cell, and limits of detection and quantification were 1.0 ng mL(-1) and 3.5 ng mL(-1) , respectively. Other interfering plants showed distinct amperometric responses. This methodology was useful to detect ∆(9) -THC even in the presence of the Fast Blue B salt, which avoided false positive results for all the studied extract plants., (© 2016 American Academy of Forensic Sciences.)